+static void ipgre_tunnel_bind_dev(struct net_device *dev)
+{
+ struct net_device *tdev = NULL;
+ struct ip_tunnel *tunnel;
+ struct iphdr *iph;
+ int hlen = LL_MAX_HEADER;
+ int mtu = ETH_DATA_LEN;
+ int addend = sizeof(struct iphdr) + 4;
+
+ tunnel = netdev_priv(dev);
+ iph = &tunnel->parms.iph;
+
+ /* Guess output device to choose reasonable mtu and hard_header_len */
+
+ if (iph->daddr) {
+ struct flowi fl = { .oif = tunnel->parms.link,
+ .nl_u = { .ip4_u =
+ { .daddr = iph->daddr,
+ .saddr = iph->saddr,
+ .tos = RT_TOS(iph->tos) } },
+ .proto = IPPROTO_GRE };
+ struct rtable *rt;
+ if (!ip_route_output_key(&init_net, &rt, &fl)) {
+ tdev = rt->u.dst.dev;
+ ip_rt_put(rt);
+ }
+ dev->flags |= IFF_POINTOPOINT;
+ }
+
+ if (!tdev && tunnel->parms.link)
+ tdev = __dev_get_by_index(&init_net, tunnel->parms.link);
+
+ if (tdev) {
+ hlen = tdev->hard_header_len;
+ mtu = tdev->mtu;
+ }
+ dev->iflink = tunnel->parms.link;
+
+ /* Precalculate GRE options length */
+ if (tunnel->parms.o_flags&(GRE_CSUM|GRE_KEY|GRE_SEQ)) {
+ if (tunnel->parms.o_flags&GRE_CSUM)
+ addend += 4;
+ if (tunnel->parms.o_flags&GRE_KEY)
+ addend += 4;
+ if (tunnel->parms.o_flags&GRE_SEQ)
+ addend += 4;
+ }
+ dev->hard_header_len = hlen + addend;
+ dev->mtu = mtu - addend;
+ tunnel->hlen = addend;
+
+}
+